title: Evolutionary relations of Hexanchiformes deep-sea sharks elucidated by whole mitochondrial genome sequences.
abstract: Hexanchiformes is regarded as a monophyletic taxon, but the morphological and genetic relationships between the five extant species within the order are still uncertain. In this study, we determined the whole mitochondrial DNA (mtDNA) sequences of seven sharks including representatives of the five Hexanchiformes, one squaliform, and one carcharhiniform and inferred the phylogenetic relationships among those species and 12 other Chondrichthyes (cartilaginous fishes) species for which the complete mitogenome is available. The monophyly of Hexanchiformes and its close relation with all other Squaliformes sharks were strongly supported by likelihood and Bayesian phylogenetic analysis of 13,749 aligned nucleotides of 13 protein coding genes and two rRNA genes that were derived from the whole mDNA sequences of the 19 species. The phylogeny suggested that Hexanchiformes is in the superorder Squalomorphi, Chlamydoselachus anguineus (frilled shark) is the sister species to all other Hexanchiformes, and the relations within Hexanchiformes are well resolved as Chlamydoselachus, (Notorynchus, (Heptranchias, (Hexanchus griseus, H. nakamurai))). Based on our phylogeny, we discussed evolutionary scenarios of the jaw suspension mechanism and gill slit numbers that are significant features in the sharks.
authors.affiliation: Department of Molecular Life Science, Division of Basic Medical Science and Molecular Medicine, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa 259-1143, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Tanaka
authors.forename: Takashi
authors.initials: T
authors.lastname: Shiina
authors.forename: Taketeru
authors.initials: T
authors.lastname: Tomita
authors.forename: Shingo
authors.initials: S
authors.lastname: Suzuki
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Hosomichi
authors.forename: Kazumi
authors.initials: K
authors.lastname: Sano
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Doi
authors.forename: Azumi
authors.initials: A
authors.lastname: Kono
authors.forename: Tomoyoshi
authors.initials: T
authors.lastname: Komiyama
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Inoko
authors.forename: Jerzy K
authors.initials: JK
authors.lastname: Kulski
authors.forename: Sho
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004272:DNA, Mitochondrial / Q000235:genetics*; D054629:Genome, Mitochondrial / Q000235:genetics; D005880:Gills / Q000502:physiology; D059014:High-Throughput Nucleotide Sequencing; D007568:Jaw / Q000502:physiology; D010802:Phylogeny; D012754:Sharks / Q000235:genetics*
chemical_list: D004272:DNA, Mitochondrial